This invention relates in general to friction clutches and in particular to an electric actuator assembly for effecting engagement and disengagement of such a clutch.
Clutches are well known devices which are frequently employed in vehicles to selectively connect a source of rotational power, such as the crankshaft of an engine, to a driven mechanism, such as a transmission. Typically, a cover of the clutch is connected to a flywheel carried on the end of the engine crankshaft for rotation therewith. Between the flywheel and the clutch cover, a pressure plate is disposed. The pressure plate is connected for rotation with the flywheel and the cover, but is permitted to move axially relative thereto. A release bearing is connected to the pressure plate such that axial movement of the release bearing causes corresponding axial movement of the pressure plate. A driven disc assembly is disposed between the pressure plate and the flywheel. The driven disc assembly is carried on an output shaft of the clutch, which forms the input to the transmission.
Means are provided for selectively moving the release bearing (and, therefore, the pressure plate) back and forth in the axial direction. When the pressure plate is moved toward the flywheel, the driven disc assembly is frictionally engaged therebetween so as to cause the output shaft of the clutch to rotate with the flywheel, the cover, and the pressure plate. When the pressure plate is moved away from the flywheel, the driven disc assembly is released from such frictional engagement so as to disconnect this driving connection. In some clutches (pull-to-release type), movement of the release bearing in an axial direction causes movement of the pressure plate in the same axial direction. In other clutches (push-to-release type), movement of the release bearing in an axial direction causes movement of the pressure plate in the opposite axial direction.
In either instance, the means for moving the release bearing axially back and forth typically includes a rotatable shift shaft which extends transversely through the clutch. The shift shaft is provided with a fork or similar structure which engages the release bearing. Rotation of the shift shaft in a first rotational direction causes movement of the release bearing in one axial direction. Similarly, rotation of the shift shaft in a second rotational direction causes movement of the release bearing in the opposite axial direction. Thus, rotation of the shift shaft causes movement of the pressure plate and, therefore, engagement and disengagement of the clutch.
To effect the rotational movement of the shift shaft, a shift arm is connected to one end thereof outside of the clutch. Thus, pivoting movement of the shift arm causes rotational movement of the shift shaft to engage and disengage the clutch. In the past, movement of the shift arm has been accomplished by means of a mechanical linkage extending between the shift arm and a clutch pedal located within the driver compartment of the vehicle. As is well known, depression of the clutch pedal caused movement of the shift arm in one direction to rotate the shift shaft, causing disengagement of the clutch. Similarly, release of the clutch pedal caused movement of the shift arm in another direction to rotate the shift shaft, causing engagement of the clutch. Also, it is known to provide a hydraulic connection between the shift arm and the clutch pedal for a similar purpose.
Although mechanically and hydraulically actuated shift assemblies as described above have been used successfully for years, it has been found desirable to provide some other means for selectively moving the release bearing and the pressure plate between the engaged and disengaged positions. Specifically, it has been found that it would be desirable to effect engagement and disengagement of the clutch by an electrically actuated shift mechanism. Such an electric actuator would eliminate the force transmitting mechanism between the operator and the clutch, resulting in a reduced number of parts, decreased assembly time, and minimal maintenance. Also, an electric actuator would relieve the driver from manually exerting a large force against the clutch pedal each time it is desired to disengage the clutch. Lastly, an electric actuator could be easily adapted for use with an electronic control system for automating the operation of the clutch in response to the operating conditions of the vehicle.